Bone conduction audiphone



June 18, 1946'. w A ZARTH 2,402,480

BONE CONDUCTION AUDIPHONE 'originl Filed April 8. 195s FIGA.

- INVENTOR. 3 [M4/AMA Z457# v amano` BONE coNDUcTIoN AUDrPnoNE William A. `Zarth, East Orange, N. J., assignor to Dictograph Products Company, Inc., New York, N. Y., a corporation oi' Delaware @riginal application April 8, 1939, Serial No. I 266,757. Divided and' this application November 7, 1941, Serial No. 418,171

l This invention relates to audiphones, and has particular reference to bone conduction audiphones having a vibratory member adapted to be placed in operative connection 'with thebone structure of the user for transmitting therethrough to the inner ear the audible sounds picked up by .a suitable microphone. This application is a division of application Serial No. 266,757, filed .April 8, 19,39, now Patent No. 2,262,082.

In general, the prior bone conduction audiphones may be divided into two classes. In one class. the electromagnetic means is supported' by a headband or the like, withl its vibratory member held in operative connection with the bone structure of the user, so that the vibrations thereof across. the magnetic'gap are normal to the bone it engages and are applied directly thereto. An example of this type of audiphone is illustrated in Patent No. 2,144,458, issued January 17, 1939, to Henry Koch. In the other class of bone conduction audiphones, the vibratory member of the electromagnetic means is supported by a headband or the like, with the relatively massive part of the electromagnetic means oatingly mounted with respect thereto, so

'that while the. vibrations across the air gap are normal to the bone surface, they are applied indirectly thereto, being reactive vibrations of the vibratory member relatively to the said massive part because oi' the high relative inertia of the latter. in example of this class oi audiphone is illustrated in Patent No. 2,l8,il2, issued February 2l, i939, to Henry Koch. While both classes of audiphone's have proven generally satisfactory, there are certain objections to each. For example, with the first, or direct-acting class, the free vibrations ofthe reed connected to the vibratory member are liableA to be suppressed to a certain degree by reason of the contact of thelatter with the bone, unless the headband pressure and the resilientconnections between the relatively vibrating parts are carefully proportioned. although it has the advantage of low powerexpenditure. With the second or inertia reaction class, the relatively heavy masses which are desirable in order to securefthe requisite vibration cause the expenditure of a considerable amount of power, although it has the advantage that neither the air gap nor the vibrations of the vibratory member are aiectedby pressure of the latter on the bone.

tioned classes of bone conduction audiphones, embodies their principal advantages and does not embody their disadvantages. In a preferred embodiment of the invention, the vibratory member adapted to be placed in operative connection with the-bone structure of the user, carries an electromagnetic means having a vibratory element which vibrates independently of the member and in a direction generally parallel to the surface of the bone which the member engages, instead of normal thereto, as in 'thecase of both classes of prior audiphones, whereby the vibrations of the member are not suppressed by its contact with the bone and the inertia of the parts is not reliedl on to provide the requisite vibration, so that less power is required.

tween the opposite ends of the ilrst core,` thereby forming a generally E-shaped structure having two flux paths and two air gaps.

It will be seen that the bone conduction audiphone of this invention is a very simple and effective device for securing efficient vibrations o the bone without expenditure of a large amount of power and without variation of the air gap, due to pressure of the receiver on the bone. Because the inertia of the electromagnetic means is not utilized during the operation of the new device, the mass thereof need not be great but only suihcient to provide an emcient iiux path to secure the vibrationsnecessary for audible and ,intelligible audition.

Fig. 4 illustrates the manner of supporting the I audiphone on a headband and the manner of connecting it in a microphone circuit.

Referring to Fig. 1 of the drawing, numeral l0 designates the contact plate, preferably of non- 3. metallic material such as synthetic resin, having a relatively substantial area on the order of one square inch, and being relatively fiat for placement in operative connection with the bone structure of the user to serve as the vibratory mem- 4ber which transmits vibrations tothe inner ear through the bone structure of the user. The contact plate I may serve as a wall of a casing. the other walls of which are provided by a hollow cover II suitably attached to the contact plate I II by screws passing through holes I2 shown The element I5 is not a completely closed ringy but the inwardly-turned ends I8 and I9 of the two upwardly extending L-shaped arms I6 and I1 are spaced apart to accommodate the free end of the third arm 2 0, which is secured in a vertical position so as to extend normally to the contact plate IIJ.

In order that the arms I6 and I1 may have the required resiliency for vibration, the base of the element I is preferably a stiff steel spring 2| having appropriate magnetic permeability. The vertical arm may be screwed thereto in the manner illustrated in Fig. 3, with the arms I6 and I1 also screwed to the opposite ends of the spring 2| in the manner shown.

The entire core constituting the L-shaped arms IB and I1 and the vertical arm 20 accordingly is generally E-shaped with narrow air gaps 22 and 23 formed between the ends I8 and I9 of the arms I6 and I1 and the corresponding op'- posed faces of the vertical arm 20. The width of these air gaps is on the order of l/woo of an air gap 22, and vertical arm 20, and the other flux path traversing spring 2|, arm I1, air gap 23 and the vertical arm 20. These two flux paths are accordingly relatively short and because of the flux density traversing the air gaps they may be made very narrow, thus enhancing the efl'iciencyvof the device. If desired, two speech coils mounted on arms I6 and I1 may be used instead of single voice coil 24, as illustrated in said copending application, or they may be additional to the coil 24, depending upon requirements.

In operation, with the contact plate III held against the bone structure of the user by means of the headband 33 pivoted thereto, and with voice currents energizing the coil 24, the arms I6 and |-1 are vibrated about the center support I3. owing to the restricted flexing of the stiff `spring 2|.

The vibration is accordingly in a di-v rection substantially parallel to the surface of the contact plate or vibratory member III, and by -reason of the aforementioned substantial leverage of the claims I3 and-I1 about fulcrum I3. there is a powerful although small component of this vibration in a direction normal to the contact plate I0, and it is this component of vibration which is transmitted to the bone. Although this component of vibration is so minute that it is practically unmeasurable, the vibrations are y powerful and are readily heard and intelligible netically permeable material constructed to be resilient about its support I3 in the manner llpicked up by the microphone 25 shown in Fig.

4, causes variation of the flux across the air gaps 22 and 23, resulting in relativevibration ofthe arms I6 and I1 about support I3 with respect to each other and with respect to the vertical arm 20.

4The voice coil 24 is connected in circuit with the microphone 25 and a source of power, such as the battery 26. and this circuit preferably includes a suitable amplifier, not shown. The contact plugs 21 in this circuit are adapted to be removably received in corresponding holes 28' in the cover II, as shown in Fig. 1. Extending into each of these holes 28 is a contact member 29 electrically connected by spring 30 to a. connectwardly and outwardly in opposing phase, said x core having a transverse dimension parallel to said surface which is at least as great as its diing strip 3|, which extends into cover II and is connected by a corresponding filament 32 to a terminal of cOil 24.

It will be observed that with this arrangement two flux paths, one traversing spring 2|, arm I8,

by deafened persons, it appearing that the comparatively large amplitudes of vibrations of the two classes of .prior bone conduction audiphones being unnecessary to good bone audition.

While certain preferred embodiments of this invention have been illustrated and described herein, it is to be understood that the invention is not limited thereby but is susceptible of variations in form and detail within the scope of the appended claims. For example, the cores I5 and I5' may be any shape with the speech coils mounted on the horizontal arms instead of the vertical arms. so long as the general direction of the vibration across the air gap is substantially parallel to the contact plate surface engaging the bone.

I claim:

. 1. In a bone conduction audiphone, the combination of a vibratory member having a bodycontacting surface, electromagnetic means comprising va core attached to said member and a winding thereon, said core having a portion extending substantially parallel to said surface and secured to said member at a zone between the ends of said portion, a pair of first arm portions extending substantially normal to and from said first portion in spaced relation and having their free ends turned inwardly, and a third arm .interposed between said rst arm portion and forming with the said inwardly turned ends thereof a pair of narrow magnetic gaps across which the said ends of said first arms relatively vibrate inmension normal to said surface, whereby a component of the said vibrator normal to said surface is transmitted to said member for conduction through the bone structure to the inner ear of the user.

2. In a bone conduction audiphone, the combination of a casing having a body-contacting portion, an E-shaped core having a middle and two end arms, said core being connected to said portion at a zone substantially in alignment with the middle of said E-shaped core, the remainder of asoman said core being spaced from said casing, inturned ends on the end arms of said member defining narrow gaps between said ends and said middle arm, a winding on said middle arm for varying the magnetic flux across said gaps when energized by voice currents to cause said arms to vibrate in opposing phase and produce a component in alignment with said middle arm for conduction through said portion and the bone structure to the inner ear.

3. En a bone conduction andiphone, the combination of a hollow audiphone casing having a wall portion for engaging the body, a core member comprising a stili?. substantially'fiat spring secured at its midnortion to said wall and extending substantially parallel thereto, arms extending outwardly in the same direction from opposite ends 0i said plate, a middle arm extending outwardly from said midportion of said plate and between said end arms, inturned outer ends on said end arms forming narrow magnetic gaps between said end and middle arms, a-winding on said middler arm adapted to`receive voice currents to vary the magnetic ux across said gaps and cause said end arms to vibrate in opposing phase, whereby a component of said vibration in alignment with said middle arm is transmitted to said wall for conduction through the bone structure to the inner ear of the user.

1 AM A. ZARTH. 

